In the past few decades, as both timber resources and available landfill sites have greatly diminished, the demand for recycling of printed papers, especially newsprint, has skyrocketed. Such recycling efforts have been aimed at developing processes whereby previously-used papers can be reprocessed and recycled for use. A major objective of such processes is the recovery of fibers which possess the physical properties and brightness of more expensive virgin pulp. End use considerations also play a major role in determining which parameters are critical for efficient recycling. Thus, for example, in newsprint ink holdout is of primary importance while in tissue, removal of fillers is critical to obtain a final product of satisfactory softness.
One major obstacle to the efficient recycling of such papers is the difficulties encountered in removing the ink from the printed paper before, during, or after the pulping process. This has become particularly difficult with newly developed inks and printing processes, which result in a much more tightly bound ink to the fibers. Improved deinking agents are needed to expand the utility of the deinking process.
The deinking process and deinking agents have been discussed in many articles (see e.g. Crow and Secor, Tappi Journal, July 1987, pp 101-100; Wasilewski, 1987 Pulping Conference Proceedings, pp 25-31; McCool and Silveri, 1987 Pulping Conference Proceedings, pp 33-39; and Gilkey et al., 1987 Pulping Conference Proceedings, pp 133-141). Briefly, all such processes involve the removal of the ink from the recycled paper by use of deinking agents such as detergents or surfactants, and the subsequent separation of this removed ink from the pulp. This separation is accomplished by washing, wherein the ink is dispersed in the aqueous system and removed with the water using mechanical processes such as centrifugation or screening, by flotation, wherein the ink is suspended in the aqueous system made hydrophobic, and subsequently "floated" away from the pulp in a froth (the froth is then drawn out of the system by a vacuum or mechanical overflow system), by mechanical means (flocculation, screening, centrifugation, etc.) or by a combination of these processes. Since none of these systems will completely remove all of the ink, the deinking agents must also contain compounds or functional groups which prevent redeposition of the removed ink on the cleaned fibers.
To date, deinking agents used in these processes have not satisfactorily fulfilled all these functions. For example, U.S. Pat. No. 4,518,459, Canadian Pat. No. 1,009,804. German Patent No. 2,903,150 and Japanese Patent Nos. 51,892/80, 117,690/82, 59,990/84, 155,794,85 and 117,690/82 disclose conventional detergents, and surfactants for use in deinking, whereas the use of a combination of surfactants and polymers is described in Japanese Pat. Nos. 75,889/86 and 85,089/87 and UK Pat. Application GB 2,178,079A (published Feb. 4, 1987). The mixtures produce a satisfactory gain in brightness of the pulp, but the pulp still contain residual ink, including large spots, which renders the pulp unsuitable for use in many applications.
Further, as new printing ink formulations and printing processes are developed, and the demand for recycling other types of waste papers (including films, foil coated papers, and pulp-colored papers) increases, there exists a real need for improved deinking agents which can effectively remove the printed ink from these furnishes.